1. Field of the Invention
The present invention relates generally to process monitoring systems and more particularly, but not exclusively, to monitoring of integrated circuit device fabrication processes.
2. Description of the Background Art
A typical integrated circuit device fabrication facility or “fab” can process semiconductor wafers at a high rate to produce various devices. It is also not uncommon for processing of a single wafer to take almost three months and for different devices to be manufactured at the same time using the same equipments. Wafers may be grouped together in lots, with each lot being carried in a pod. All wafers in a pod are typically of the same kind (e.g., same devices). Some of the lots may be inspected using specific metrology equipment to observe some wafers in the lot. The observations provide defectivity measurements. For example, 4 or 6 wafers in a lot of 25 wafers may be chosen for inspection to obtain defectivity data. Typically, only a small proportion (e.g., 20%) of the lots is selected for inspection. FIG. 1 shows example defectivity observations on a semiconductor wafer 100.
While workable, the just-described monitoring procedure allows only a very small portion of the production to be observed. Moreover, because defectivity operations do not directly relate to device production, operators are inclined to bypass them.
Defectivity metrology measures isolated defects and produces observations, such as number of defects of a minimal size, defect density, and a proportion of dies affected by the defects on the wafer area. These defects are responsible for almost 80% of the yield loss in a fabrication facility for a mature product. Embodiments of the present invention allow for global predictive monitoring of a fab or other manufacturing facility to look for trends that can negatively impact the yield.